First and foremost we ought to recall how a sizeable number of Iranian Leftists were viciously and mercilessly physically eliminated in mass executions of early and late 80's (1983 and 1988).
Also let's not forget how this process of extreme violence utilized in elimination of Iranian Leftists began right after the establishment of mullahs' totalitarian theocracy in 1979 and continues to this very day.
The obvious point about such reminder is to fully appreciate and comprehend the fact that Iranian Left didn't just "slowly disappear" but has been violently forced off from the center stage of Iranian social scene, where it has always belonged.
However as much as Iranian Left has been subject to this murderous process of state violence it has never really "disappeared into a mysterious ether" but has always had a presence in Iranian society, culture and politics; mainly through contemporary Iranian social movements (encompassing Students, Women, Labor, National-Minorities, Alternative Arts...movements). Perhaps describing this process as a case of displacement rather than disappearance might be a more accurate description.
Keeping in mind how two generations of Iranian Leftists (pre-1979 generation and the generation which commenced its activism in or around 1979) were physically wiped off the social map in our land, it is amazing how Left still has such a presence in various social justice movements in Iran; which is mainly due to excessive economic inequalities of the past two decades.
A concluding query might be: Could Iranian Left make a drastic comeback in the near future and become a major visible social force in our land again?
And a reasonable retort could be: It would depend on the balance of social forces in Iran and even then majority of activists still would have to operate in strict semi-clandestine mode of activism.
Meanwhile we should all rest assure that reports of Iranian Left's death are greatly exaggerated.

The picture below is from a 16th of Azar demo in Tehran university. One of the placards reads: "Socialism or Barbarism."

Demonstration in Tehran University against privatization of Higher Education- Dec 2015

Why Iran's left is dead you ask?
Iran's left is not dead but has been going through the diffusion stage for the following reasons:
- Soviet Union is gone and China has gone through metamorphosis, those groups who aligned themselves with these 2 poles have lost their sponsors, hence diffused.
- The pre revolution generation of Marxists have died out due to old age and the new generation never had a chance due to the wholesale repression imposed on them by the Velayat Faghigh.
- Orthodox Marxism as an ideology for change has run its course due to the changing situations and new equations in human history.
- The struggle for social justice is alive and well in Iran and all over the world and will continue for obvious reasons. This struggle is more inclusive and has new participants and leaders

This article reports on how some Turks see Erdogan's recent extreme crackdown as a "witch hunt of medieval darkness."
But medieval darkness has always been a central component of Islam whether in Iran, Afghanistan, Pakistan, Saudi Arabia,...a superstitious, violent darkness follows Islam wherever it is.

In fact, you're the one who called Arabs "M.F" because they destroyed and burned Iran's libraries, buildings... etc. .. NOT me.
Also "the idea for creation of "Eretz Israel" was NOT first developed by .... in 1840's". it was first developed from Tanakh at 1 Samuel 13:19 following the Exodus when Israelite tribes were already in the land of Canaan. It is a biblical term, way before than 1800.
Ottoman empire collapsed after WWI. The land was under control of Ottoman empire for 1000 years. From the time of Umar. Sykes-Picot Agreement gave the full control of the land to British. Brits decided to settle Holocaust survivals in that land.

Iran and Germany had close ties during the time of Nazi party. common knowledge. There were 3000 German families who were living in Iran during that time. They contributed a lot to Iran's infrastructure. Unlike Americans in Vietnam or other places, German came to Iran with their families and they were all respectful. They built the most famous building such as Iran central bank بانک مرکزی ایران در خیابان فردوسی or the bridges such as Versak پًل ورسک Tunnels such as Kandawan. تونل کندوان
So what ?
Is that surprise you ?
Is that mean Iranians were against Jews or Israel. ? No, I don't understand where you got such an idea.
F.Y.I
There is an area close to Rah Ahan which is called "Nazi Abad" and t's named after Nazi Germany because of German's contribution to Iran's infrastructure, especially in southern Tehran.
Because of Qajar treasurous treaty with British, Iran was robbed by English.
Oil concession was signed by Mosaddeq's opium addict uncle known as Mosafardin Shah in 1901. Iran was screwed by British, so Iranians felt close to German in reaction to British robbery of their country. Is that surprise you.?
Is that mean that Iranians were against Jews ? NO,
Again, it is common sense.
Did I say some people from 1970's show very poor judgement once it comes to politic ?

This is f-en huuuge. IRI couldn't spend enough $$$ on PR, marketing, lobbying to receive this sort of public relations coup. It's not quite as sweet as being handed Iraq, but dayuuuum Gina, this is pretty bootylicious. A retired four-star general in the United States Army and former Secretary of State just confirmed to the world that Israel has nuclear weapons and that *drum roll* they're all pointed towards Iran! The fallout: Other nations will be less critical of Iran building up its military and probably more critical of Israel moving forward. More fallout: Rafsanjani just tucked his Johnson between his legs *d'oh* for suggesting that Iran cut back its military spending.

Thanks for this article.
There's also this really useful and great site in Persian dedicated to issues of Domestic Violence, definitely worth a glance and visit by all Persian speaking members of the community. Thanks again.

All of this is actually very old news.
Many Iranian officials have responded to such infantile threats, with similarly infantile threats of their own, pointing out that while IR might not have nukes, it's is still fully capable of raining hell (through its long-range and mid-range missiles) on the heads of anyone stupid enough to attack Iran.
Once again proving the fact that a militarized Jewish theocracy is essentially the same as a totalitarian Shia theocracy.
They both need to have permanent crisis and chaos in order to survive.

The idea for creation of "Eretz Yisrael" was first developed by Mosses Hess in 1840's, almost a century before Holocaust.
And even after that the world Zionist movement considered many other location to settle its base, including Brazil.
Balfour Declaration of 1917 by Brits was the first building block of Zionist colonization of Palestine. But criminal monarchists are not too keen to blame their colonial masters for such crimes.
Your continued rabid racism towards our Arab sisters and brothers is appalling, shameful and unacceptable.